There are various beam shaping techniques in the art which are used for shaping the profile of light beams (such as laser light beams) of different wavelength ranges. Techniques, based on refractive and/or diffractive beam shaping components, utilizes dual-/multi-element coherent beam shaper that includes two optical elements manipulating the intensity distribution and the phase of a coherent light beam.
The principles of the refractive beam shaping technique are described for example in U.S. Pat. No. 3,476,463 to Kreuzer et al. According to this technique rays of an input beam of coherent light are redistributed to yield an output beam of different predetermined intensity distribution. The optical path lengths of the rays are maintained constant between an equiphase surface of the input beam and a desired equiphase surface of the output beam having the predetermined intensity distribution. At least two active surfaces, usually aspherical, are employed. Design equations are given for a two-element system which converts a collimated input beam of Gaussian distribution into a collimated output beam of uniform distribution.
Other techniques, referred to herein as attenuating beam shaping techniques utilize an optical filter to differently attenuate light rays of the light beam to be shaped and thereby accomplish the beam shaping. Typically, in such beam shaping techniques, specifically designed spatially inhomogeneous neutral density (ND) optical filter(s) is used to attenuate and shape the intensity distribution of light beams (i.e. the one or two dimensional lateral intensity profile of the light). The spatial distribution of the filtration properties in the filter are designed in accordance with the lateral intensity distribution of the incoming light beam and the desired lateral intensity distribution to be obtained in the output.
FIG. 1, is illustrating schematically the operation of a known in the art attenuating beam shaping system typically used in shaping beams of deep-ultraviolet light. This system utilizing specifically designed ND filter ND together with an appropriate beam blocker BB (e.g. aperture) element. The ND filter and the blocker are designed for generating un-even attenuation to the intensity of an incoming light beam having a Gaussian lateral intensity distribution, for forming an output light beam having flat (top-hat) intensity distribution over the width of the output light beam. Here, the neutral density optical filter is designed to provide higher attenuation (lower transmission) for light intensity near the center of the light beam and higher transmission closer to the edge of the light beam (the edges themselves are delimitated by the mechanical aperture).